In order to explore the possible role of the inferior colliculus (IC) in the encoding of communication signals, I am proposing to conduct a series of experiments involving behavioral, neurophysiological, and neuroanatomical techniques. The behavioral experiments are designed to record and catalogue at least some of the communication sounds used by Mexican free-tailed bats and to determine the social context in which the sounds are used. The neurophysiological experiments will examine the neuronal response features of individual neurons evoked by electronically generated sounds having power spectra similar to those of ther natural communication sounds. Furthermore, I intend to evaluate and compare how neurons in the lateral (communication) and medial (echolocation) regions of the IC respond to natural communication sounds that were previously recorded and then played back on tape loops. Finally, the neuroanatomical studies will utilize the retrograde tracer, horseradish peroxidase, to trace the inputs which project to the lateral and medial regions of the IC.